Oxides of niobium and processes for making them and their derivatives have received relatively little attention for use as refractory materials. This is principally because Nb.sub.2 O.sub.5, the most commonly encountered oxide, is not highly refractory. It melts at 1450 degrees Celsius and suffers considerable loss of oxygen near this temperature. Other oxides of niobium, e.g., NbO and NbO.sub.2, have received relatively little attention because they are difficult to prepare. As a result, the use of NbO.sub.2 as a novel starting material for any binary and higher-order mixtures with other oxides has not been extensive. Because of this, difficulty there has been limited use of such materials. There is need, therefore, for a better procedure for preparing NbO.sub.2 in order to better exploit the use of oxides of niobium and its derivatives.
Heretofore, the obtaining of NbO.sub.2 has been achieved in a variety of ways such as the reduction of Nb.sub.2 O.sub.5 by hydrogen, which reaction is also reversible. Also, by heating Nb.sub.2 O.sub.5 in a current of argon at 1150 degrees Celsius, the dissociation of the pentoxide is appreciable. For use in X-ray studies, single crystals of NbO.sub.2 have been prepared by melting pressed tablets of Nb.sub.2 O.sub.5 and metal powder, correctly proportioned, in an electric arc furnace.
Niobium dioxide prepared as described is known to have a tetragonal crystal structure as its most common polymorph, a variant of the rutile structure of TiO.sub.2 Zircon, ZrSiO.sub.4, is also a tetragonal oxide material, which structure is useful in several applications. Therefore, it may be projected useful applications would be found for NbO.sub.2 provided it were more directly and economically available.
Due to its complicated electronic structure, it has been used or proposed in such applications as secondary lithium batteries, fuel cell catalyst, photoelectrochemical cell anode, and as a thermochromic material.
Japanese Patent 89-128355 describes the use of NbO.sub.2 in batteries which exhibit a high capacity and a long cycle life. The use of NbO.sub.2 is also described in PCT number 87-07422 for an interference film component in a magneto-optical recording disk. Some of these uses include NbO.sub.2 alone or in combination with other metals or metal oxides. Nevertheless, mixtures of NbO.sub.2 with other oxides have not been studied extensively since it is first necessary to produce NbO.sub.2 as a powder, then to combine it with another material and heat it to elevated temperatures for prolonged times to generate a new material. There is, therefore, a need for a process which generates NbO.sub.2 at a high thermal plateau, so that it can react readily.